Currently, implantable medical devices (IMDs) utilize one or more electrically-conductive leads (which traverse blood vessels and heart chambers) in order to connect a canister with electronics and a power source (the can) to electrodes affixed to the heart for the purpose of electrically exciting cardiac tissue (pacing) and measuring myocardial electrical activity (sensing). These leads may experience certain limitations, such as incidences of venous stenosis or thrombosis, device-related endocarditis, lead perforation of the tricuspid valve and concomitant tricuspid stenosis; and lacerations of the right atrium, superior vena cava, and innominate vein or pulmonary embolization of electrode fragments during lead extraction. Further, conventional pacemakers with left ventricle (LV) pacing/sensing capability require multiple leads and a complex header on the pacemaker.
A small sized IMD has been proposed that mitigates the aforementioned complications, termed a leadless pacemaker (LP) that is characterized by the following features: electrodes are affixed directly to the “can” of the device; the entire device is attached to or within the heart; and the LP is capable of pacing and sensing in the chamber of the heart where it is implanted.
The LPs that have been proposed thus far offer limited functional capability. The LP is able to sense in one chamber and deliver pacing pulses in that same chamber, and thus offer single chamber functionality. For example, an LP device that is located in the right atrium would be limited to offering AAI mode functionality. An AAI mode LP can only sense in the right atrium, pace in the right atrium and inhibit pacing function when an intrinsic event is detected in the right atrium within a preset time limit. Similarly, an LP device that is located in the right ventricle would be limited to offering VVI mode functionality. A VVI mode LP can only sense in the right ventricle, pace in the right ventricle and inhibit pacing function when an intrinsic event is detected in the right ventricle within a preset time limit.
It has been proposed to implant sets of multiple LP devices within a single patient, such as one or more LP devices located in the right atrium and one or more LP devices located in the right ventricle. The atrial LP devices and the ventricular LP devices wirelessly communicate with one another to convey pacing and sensing information there between to coordinate pacing and sensing operations between the various LP devices.
A master/slave relationship may be used to coordinate pacing and sensing operations between the multiple LP devices. A strict master/slave configuration, however, requires that, for example, an “atrial pace” (“AP”) command be transmitted from the master ventricle LP to the slave atrial LP at a time when the ventricle may be in a vulnerable period. These AP commands could in theory have a risk of inducing premature ventricular excitations, which under worst-case consideration, could degenerate into sustained ventricular tachycardia or ventricular fibrillation, which may be lethal to the patient.